1. Field of the Invention
The present invention concerns an ionization flow-metering pickup and its associated electronic processing equipment, which taken together constitute a device for measuring the volume flow of a stream of gas by means of the displacement of ions along trajectories which are largely parallel to the stream.
The flow-metering pickup of the present invention is a transit-time anemometer type which is designed for measuring an air flow with a view to controlling the richness of the air-fuel mixture fed into an internal combusion engine.
2. Description of the Prior Art
The principle of transit-time anemometers is well known to specialists. It consists in measuring the time it takes for a jet of ions, induced to travel at the same velocity as the gas stream, to travel between an emission electrode and a receiving electrode. The emission electrode is a point which receives a brief, high-tension pulse which causes the ionization of the gas in its vicinity. The cloud of ionized gas thus formed gives off an electric pulse which is detected when the cloud passes a receiving electrode.
The application of such transit-time anemometers to the measurement of the intake flow in a thermal engine poses a number of difficulties.
The amplitude of the signal detected by the receiving electrode depends both on the velocity of the gas stream and the ionization conditions, i.e., the amplitude of the high-tension pulse and the nature of the emission point. The electrical data obtained thus depends on several parameters, which complicates electronic processing.
In addition, the cloud of ions is generally created by a single emission point. The rate of ionization is hence quite low, which, at a slow stream velocity, yields an electrical signal at the receiving electrode which is difficult to use. This limits the measurement capability of the pickup. The cloud of ions is not uniformly distributed through the cross section of the fluid stream vein, resulting in a measured velocity which is not representative of the average velocity of the gas stream.
In this type of pickup, for a given geometric and for a rather high stream velocity, the width of the high-tension impulse which creates the cloud of ions is no longer negligeable as against the time of passage of this same cloud of ions. The phenomena of emission and cloud displacement are superimposed, which constitutes an additional factor of error.
The present invention makes it possible to avoid these drawbacks. Its subject is a structure for the embodiment of a transit-time ionic pickup associated with an electronic device which makes it possible to obtain an electrical magnitude in the form of a pulse whose width depends on the volume flow stream of the gaseous fluid in the intake manifold.